1. Field of Invention
This invention relates to medical valves which are implanted in the human body, particular to such a valve which is easy to manufacture, performs reliably, is easy to surgically implant in the human body, and will remain functional for the life of the patient in which it is implanted.
2. Background Discussion
Medical valves are used for many different types of applications. One such application is to treat glaucoma by allowing aqueous humor to flow from the intraoccular chamber of the eye to relieve excess pressure. Thomas C. White in U.S. Pat. No. 4,554,918 has suggested one type of glaucoma valve where the aqueous humor flows from the intraoccular chamber through a tube into an external reservoir. The end of the tube in communication with the reservoir has a small opening in its end. The small opening provides a great deal of resistance to flow of the aqueous humor which is highly viscous. The White valve provides for flow in only one direction, namely, from the intraoccular chamber of the eye to the external reservoir. Upon being filled, the reservoir is pressed by the patient to force the aqueous humor contained in the reservoir through another tube into the body of the patient where it is absorbed.
Another device used to treat glaucoma is discussed by Anthoney C. B. Molteno in U.S. Pat. No. 4,457,757. This device includes a plate having a tube that extends into the intraoccular chamber. The aqueous humor from the intraoccular chamber flows onto the surface of the plate and is absorbed by the body. The Molteno plate does not have any pressure controlling mechanism, and it is only a device for releasing intraoccular pressure.
Both of these devices have been used to treat glaucoma, but the White valve suffers from the disadvantage that the patient must manually press the reservoir in order to force the aqueous humor collected in the reservoir to escape and be absorbed by the body. Moreover, although the White valve is designed to open when the intraoccular pressure becomes excessive, the valve's structure is not reliable, because it depends upon a tiny opening in the end of the tube which is very small in diameter and can easily be clogged by particulates. Nor is the White valve very sensitive, because it does not respond to slight changes in pressure to open and close. The Molteno plate overcomes the objections of the manually actuated reservoir, however, it does not employ a valve and could lead to hypotony, that is, the loss of aqueous humor within the intraoccular chamber of the eye.